Field of the Invention
The present disclosure relates to an electrophotographic photoconductor, an image forming apparatus, and a process cartridge.
Description of the Related Art
In recent years, organic photoconductors (OPC) have often been used instead of inorganic photoconductors in copiers, facsimile machines, laser printers, and multifunction peripherals in which these machines are combined, because organic photoconductors have good performances and various advantages. The reasons for these advantages include, for example, (1) optical properties such as a wide light absorption wavelength range and a high absorption amount, (2) electric properties such as a highly-sensitive, stable charging property, (3) a wide selection range of materials, (4) ease of production, (5) a cost-saving property, and (6) nontoxicity.
Meanwhile, reduction of the diameter of electrophotographic photoconductors has proceeded along with the recent trend for downsizing image forming apparatuses, and there have also been tendencies toward machine acceleration and maintenance-free. Hence, electrophotographic photoconductors have come to be expected to have a longer life span and electrostatic property stability such as a long-term non-fluctuation of the electrostatic property.
Commonly known typical electrophotographic photoconductors include undercoat layers and photoconductive layers in this laminating order over conductive supports. In common photoconductive layers, charge generating layers and charge transport layers are laminated in this order. Many of these constituent components are formed of organic compounds. Organic compounds gradually deteriorate through repetition of charging/exposure processes in the electrophotographic process, and have constituted one factor for degradation of the electrostatic property. Moreover, it has been found that in the electrophotographic photoconductors having the multi-layer configuration described above, the charge transport function of each layer and the charge injecting property at the interface of each layer have relation with degradation of the electrostatic property due to repetitive use. For example, it has been known that when there is a discrepancy between the HOMO level of the charge generating material used in the charge generating layer and the HOMO level of the charge transport material used in the charge transport layer, there occur electrostatic property changes due to repetitive use. Likewise, when the undercoat layer has a poor charge transport property or when the charge injecting property is poor between the charge generating layer and the undercoat layer, there occur electrostatic property changes due to repetitive use as in the case described above. Furthermore, the undercoat layer is deeply related with the charging property of the electrophotographic photoconductor. When the charging property related with the undercoat layer has a poor stability, the electrophotographic photoconductor undergoes charging property changes due to repetitive use.
The electrostatic property and the charging property that are related with the undercoat layer are conflicting properties, and it is extremely difficult to satisfy both of these functions. So far, attempts to improve one of these properties have often resulted in degradation of the other of the properties. As a measure for satisfying both of these functions, there have been proposed methods of improving a charge injection inhibiting function using a silane coupling agent containing an amino group (for example, see Japanese Unexamined Patent Application Publication No. 08-166679 and Japanese Unexamined Patent Application Publication No. 11-133649), and methods of adding additives such as an electron transport substance and an acceptor compound in the undercoat layer (for example, see Japanese Unexamined Patent Application Publication No. 2012-58597 and Japanese Unexamined Patent Application Publication No. 2006-030700). Particularly, Japanese Unexamined Patent Application Publication No. 2006-030700 proposes use, over a conductive support, of an undercoat layer containing metal oxide particles to which an acceptor compound (a hydroxyanthraquinone-based compound or an aminohydroxyanthraquinone-based compound) is attached. This makes it possible to obtain a stable electric property even in a long time of use, and to sufficiently prevent occurrence of leakage even if a foreign matter occurring from a member surrounding the electrophotographic photoconductor or dust entering the electrophotography apparatus from outside sticks in the electrophotographic photoconductor. However, the hydroxyanthraquinone-based compound and the aminohydroxyanthraquinone-based compound have a high crystallinity. Therefore, when these compounds are attached to metal oxide particles, the metal oxide particles tend to aggregate with each other. This makes the dispersion state in the undercoat layer nonuniform, and the electric property in a long time of use cannot be sufficiently stable.